Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 241540
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1040 AM CDT TUE MAY 24 2016

.DISCUSSION...
At 13z, surface high pressure was located over the SE U.S. with a
trough of low pressure in the lee of the Rockies. The pressure
gradient has tightened and stronger winds expected this afternoon
with conditions becoming breezy. Low level moisture continues to
stream into the area beneath a weak capping inversion near 700 mb.
12z soundings support max temps in the lower 90s but cloud cover
and winds should shave 4-6 degrees from thos values. Current
temperature forecast looks on track. There is some weak convegence
noted in the 850-700 mb layer over the eastern half of the CWA and
this is where both the RAP and HRRR develop some light showers
between 17-22z so bumped pops up to 30 percent over the extreme
east. Rest of the forecast looks on track so no other changes
planned. 43


&&

.PREV DISCUSSION... /ISSUED /

AVIATION...
MVFR cloud deck to our west is trying to filter into our area
early this morning. Already seeing some of these ceilings (and
even a few IFR level decks) edging into some of our TAF sites.
Expect to have most sites rise from MVFR to VFR later this
morning. Majority of locations should be VFR this afternoon with
possibly gusty south southeast to southeast winds. An isolated
shower or two could develop, but not confident enough to mention
in any TAF sites at this time.  42

PREV DISCUSSION... /ISSUED /

DISCUSSION...
Warm and humid conditions continue this morning with temperatures
in the low 70s and high clouds moving across SE Texas. Latest
surface analysis has weak low pressure in SW Kansas and SE
Colorado. Pressure gradient across SE Texas is not too tight but
still enough to support some light winds this morning. Winds are
stronger offshore in the Gulf of Mexico where 15 knot winds are
common. Water vapor imagery shows an upper level low off the coast
of the mid-Atlantic states. Upper level ridging stretched from SE
Texas towards the Great Lakes. Another upper level low was
organizing over California as a couple lobes of vorticity look to
merge. This system will be responsible for upcoming thunderstorm
chances on Friday.

Today and Wednesday the forecast is very similar to that of
yesterday. There may be a few isolated showers and thunderstorms.
The 00z CRP sounding did show a weak cap from the EML around
750-700mb. Models show upper level ridging building as 500mb
heights increase over the region through Wednesday. This ridging
will be in response to upstream troughing over the Desert SW.
Moisture levels gradually increase today into Wednesday so will
keep mention of an isolated storm in the forecast with 20 PoP.

Upper level low over the southern Rockies slowly moves into the
Plains Thursday into Friday. Timing of the upper low moving into
the Plains has become more consistent between the GFS/ECMWF with a
slow progression and negative tilt on Friday. This means there
will be large scale ascent to weaken capping from the EML. The
upper level jet becomes more favorable with one jet streak
becoming south/north oriented over the Plains placing E Texas in
the right entrance region. Meanwhile the southern branch of the
jet moves across Mexico into S Texas with SE Texas in the left
entrance region. Flow at 850mb increases to around 30 knots off
the Gulf of Mexico and even becomes a bit convergent. Precipitable
water values increase to 1.8 inches on Thursday and then over 2
inches on Friday which is more than previous forecasts. CAPE
should reach 2000-3000 J/Kg across the area combined with decent
low level shear of 10-20kts. Deep layer shear will be increasing
during the day to around 30-40kts. Shear parameters should support
organized convection. The overall pattern along with deep moisture
supports a heavy rainfall threat. Models are really hitting north
Texas hard with precipitation and then bringing higher QPF into SE
Texas late Friday. Most likely axis of heavy rainfall will
stretch from Columbus west of Houston NNE to the Arklatex region.
It is possible for most of the heavy rainfall to be north of
Houston but any mesoscale boundary that develops south of the main
convection could push into the Houston area. It would then be
possible for mesoscale processes to become dominate and given
strong inflow from the Gulf, heavy rainfall could shift farther
south into Houston. Again this is an alternate scenario dependent
on the mesoscale evolution that will be difficult to resolve. On
top of the heavy rainfall threat, severe weather may be possible
given the CAPE/shear combinations. Hail and downburst winds would
be the main hazards but there may be a small tornado threat if
there is enough low level shear.

For the weekend, thunderstorm chances will linger but lower
chances than Friday. While overall moisture decreases with
precipitable water values under 1.7 inches for the weekend, the
atmosphere may still be weakly capped that diurnally driven
convection could still develop. Thunderstorm activity may become
more widely scattered on Saturday with more isolated activity
expected Sunday/Monday.

Overpeck

MARINE...
Winds and seas will continue to slowly strengthen through the week
in response to a tightening gradient between lower pressures in the
lee of the Rockies and higher pressures off to our east. Caution
flags over the offshore waters may need to be expanded these next
few days, and advisories might be needed. Look for decreasing winds
and seas over the Memorial Day weekend.  42

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      88  74  88  74  84 /  20  10  20  10  50
Houston (IAH)              87  75  88  75  86 /  20  10  10  10  30
Galveston (GLS)            84  78  83  78  83 /  30  10  10  10  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION through Wednesday morning
     FOR THE FOLLOWING ZONES: Coastal waters from Freeport to
     the Matagorda Ship Channel out 20 NM...Coastal waters from
     High Island to Freeport out 20 NM...Waters from Freeport to
     the Matagorda Ship Channel from 20 to 60 NM...Waters from
     High Island to Freeport from 20 to 60 NM.

&&

$$

Discussion...43


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